The present invention relates to a sleeping bag device which is suitable for bivouac use during mounting climbing, hiking and so forth.
In general, a sleeping bag device has an elongated inner chamber or cavity for accommodating the user's body, and warmth-retaining means surrounding the inner cavity and having a head opening serving as an entrance/exit which enables the user to enter and leave the inner cavity. Usually, the warmth-retaining means has a layer of heat-insulating material such as cotton which fills a space defined between inner and outer water-proof cloth lining sheets. The heat-insulating material is suitably quilted by sewing both cloth liner sheets so that local concentration of the heat-insulating material due to movement thereof is avoided.
A gap is inevitably formed between the user's body as it lies in the sleeping bag device and the warmth-retaining means, more precisely, the inner cloth lining sheet. Obviously, a smaller gap provides a higher warmth-retaining efficiency. Unfortunately, no sleeping bag device so far proposed includes measures for positively reducing the size of this gap. When the user turns in sleep, some of the air in the gap is forced out of the sleeping bag device to dissipate heat with the result that the warmth in the sleeping bag device cannot be efficiently retained. This problem is particularly critical where the size of the user's body is small relative to the size of the sleeping bag device.